Fingerprint-based personal identification requires having a person to be identified to press his/her finger on a sensing circuit, obtaining a two-dimensional analog image of the finger, converting the two-dimensional analog image into a two-dimensional digital image datum, for example a two-dimensional pixel datum, and reading the whole two-dimensional digital image datum for comparison with stored datum for identification. However, after the sensing circuit obtains a two-dimensional analog image, it needs yet to identify in advance if the obtained two-dimensional analog image is exactly an image of a real finger's print, and the personal identification by using the obtained two-dimensional analog image is only executed after the obtained two-dimensional analog image is verified as a fingerprint image, so as to prevent mis-operation. For this purpose, the existing approaches usually use a preset standard parameter to verify a fingerprint's image. Although a standard parameter may effectively work for most people, there are still some people may fail to be identified under the same standard parameter due to various conditions, for example a very-dry finger or a finger not having enough clear fingerprint.
Therefore, it is needed alternative methodology of fingerprint detection effective for all kinds of fingers.